Force exerted by water on diver (2nd law of Motion)

AI Thread Summary
A physics student is struggling with a problem involving a high diver who jumps from a height of 9.5 m and enters the water, where his downward motion is stopped after 5.92 seconds. The student initially calculates the acceleration of the water on the diver but receives an incorrect answer when submitting it online. A suggestion is made to find the diver's velocity just before entering the water using conservation of energy, rather than assuming it is zero. This approach helps clarify the calculations needed to determine the average upward force exerted by the water. The discussion emphasizes the importance of accurately accounting for the diver's velocity upon entering the water.
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I've been in my physics class for almost two months now, and I'm starting to run into trouble. I think I'll be around here for a while, assuming you guys can help me out ;)

The Question : A high diver of mass 68.4 kg jumps off a board 9.5 m above the water.
The acceleration of gravity is 9.8 m/s2 .
If his downward motion is stopped 5.92 s after he enters the water, what average upward
force did the water exert on him?
Answer in units of N.

Homework Equations

:
v = v0 + at (To determine acceleration
EF (Average Force) = ma

The Attempt at a Solution

:
Well, I first have to find the acceleration of the water on the swimmer :
v = v0 + at
0 = (9.5m*9.8m/s^2) + a (5.92)
-93.1 = a (5.92s)
-15.726 m/s^2 = a

Now I plug that into F = ma
F = ma = (68.4 kg) (-15.726 m/s^2) = -1075.682 N

This looks about right, but when I put it into Quest, it comes out wrong. I've checked my math over twice. What am I doing wrong?

Thanks for the help :)
 
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you put t=5.92, but that is for when he now enters the water.

so in v=u+at

we want v=0, but the diver doesn't enter the water with 0 velocity. So you need to find this velocity 'u'. (try using conservation of energy to find this velocity)
 
Thank you very much - that helped me a bunch ;)
 
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